You can do this with drivers, and I've seen multiple blender channels that use an empty to control the value of multiple lights.
i was wondering how i would use drivers to control the value of multiple math nodes within the margin of -1 to 2 with an empty's z location. the reason i want to do this is because i need to control the transparency factor of multiple objects but only in the viewport so that means not an animation. also, what i mean by "within the margin of -1 to 2" is that if i move the empty up then the value will only increase up to the value of 2 then after that point, no matter how much i move the empty up, the value wont go past 2.. and same with the -1 value.
there is an equation out there that lets us do this but i have yet to find it. :( you don't have to tell me the whole equation i just need some better insight on how i would achieve this or maybe someone's experience using a similar driver setup in there own projects. thanks.